Interactive RegEX tool?

Hi!
Does anyone know if there are any interactive tools for fiddling with regex's and source texts? I whipped one up for myself a while ago; among other things it allows switching between standard regex options (singleline, mutliline, case-insensitive etc), and lets me keep history of expressions that I've tried, and lets me directly copy out of the source text that I'm working with.
If anyone's interested, I might put the code on CodePlex, or make it an online app on my server...
Stephen Lowe
disclaimer: though I work for Microsoft as an Architect Evangelist, my opinions (and occasional errors) are my own.